1. Field of the Invention
The present invention relates to a linear motion guide unit with lubricating plate assemblies, which is applicable to industrial robots, semiconductor manufacturing apparatus, precision instruments, machine tools and the like.
2. Description of the Prior Art
The linear motion guide units have conventionally incorporated in the parts or components of industrial robots, semiconductor manufacturing machines or the like, where the precise control is required for reciprocating motion. The recently remarkable development in mechatronics technology extensively requires linear motion guide units. In addition, the linear motion guide units recently became required to meet with needs of increasingly severe operating conditions. For instance, the robots for assembling are now manufactured in various types, from a large scale to a miniature in accordance with the expansion of their usage. The linear motion guide units to be incorporated in such assembling robots become required to meet with needs of maintenance-free, along with miniaturization, high precision and high speed in operation. To cope with the needs, the linear motion guide unit has required the self-lubrication of long service life on its relatively movable sliding areas.
A linear motion guide unit as shown in FIG. 21 in perspective is conventionally well known and, for example, disclosed in Japanese Patent Laid-Open No. 237113/1987. The prior linear motion guide unit is what is referred to as a ball-spline bearing and composed of a track shaft 2 of a substantially circular cross section, and a cylindrical sliding element, or a slider 1, mounted on the track shaft 2 for sliding movement. The track shaft 2 has on an outer circumferential surface thereof three lines of ridges 3 extending axially of the shaft. Raceway grooves 4 formed on the track shaft 2 are arranged in the opposite sides of the ridges 3, two grooves to each ridge. The slider 1 includes a casing 5 movable along the track shaft 2 and end caps 6 attached to the casing 5. Moreover, the casing 5 is of a hollow cylindrical member, the inner circumferential surface of which is formed with raceway grooves 7 confronting the raceway grooves 4 on the track shaft 2 to thereby define load raceways therebetween for allowing rolling elements 8 to run therethrough. Thus, the slider 1 may move on the track shaft 2 in a sliding manner by virtue of rolling elements 8 running through the load raceways. A key way 14 is formed on the outer surface of the casing 5 for mounting other appliances or the like.
The casing is provided therein with return passageways 9 extending in parallel with the associated raceway groove 7. The end caps 6 are each provided therein with claws, not shown, for scooping the rolling elements 8 out of the raceway grooves 4, 7 and turnarounds 10 to turn the rolling elements 8 for endless circulation. Mounted on the end caps 6 are end seals 11 and both the end caps 6 and the end seals 11 are mounted to the casing 5 by retaining rings 12, or cir-clips. The end seals 11 are made of core metals and rubber members of, for example, acrylonitrile-butadiene rubbers for closing clearances between the track shaft 2 and the lengthwise opposing ends of the slider 1 thereby protecting the working area in the slider 1 from dust and dirt.
The load raceways defined by the confronting raceway grooves 4, 7, non-loaded turnarounds 10 formed in the end caps 6 and non-loaded return passageways 9 formed in the casing 5, in combination, constitute endless-circulating paths for the rolling elements 8. That is to say, in practice, the rolling elements 8 may run from the raceways into any one of the lengthwise opposing turnarounds 10 in the end caps 6, then through the return passageways 9 in the casing 5 and the other of the turnarounds 10, and circulate to the raceways. Thus, the rolling-contact of the rolling elements 8 with the load raceways may help ensure the smooth movement of the slider 1 relative of the track shaft 2.
In the prior linear motion guide units, grease or lubricating oil is commonly used for lubricating the confronting raceway grooves 4, 7 and the rolling elements 8.
To lubricate the raceway grooves 4, 7 and the rolling elements 8 in the linear motion guide unit constructed as described above, grease or lubricating oil is commonly employed. In case of grease, it is applied to the raceways for the rolling elements 8 through grease nipples mounted to the end caps 6 or through an oiling hole 13 provided at the outer peripheral surface of the casing 5 so as to communicate to the return passageways 9. In contrast, lubricating oil is also to the runways through the oiling hole 13.
Nevertheless, as the linear motion guide units such as linear rolling motion guide units and ball nut and screw assemblies becomes recently more common, wide applications in various fields, they are increasingly used under unfavorable operating conditions or adverse environments, for example, where no replenishment of lubricating oil is allowed, much dirt and debris may occur and there is abnormally high in temperature or moisture. In recent years much attention has been thus given the development of the linear motion guide units having no fear of lubrication failures even under the severe operating conditions, where it is very hard to achieve the normal lubrication. Disclosed in, for example, Japanese Utility Model Laid-Open No. 4593/1995 is a ball nut and screw assembly including lubricant-containing polymer to ensure the satisfactory operation even under the unfavorable environment where it might be plagued with the difficulties of lubrication. The prior ball nut and screw assembly cited above is composed of a screw shaft having helical external grooves around the outer periphery thereof, a nut fitted loosely over the screw shaft and provided on the inner surface thereof with helical internal grooves confronting the grooves on the screw shaft, balls running through helical spaces between the confronting helical grooves, and lubricant-containing polymer members arranged so as to make slide-contact with the helical groove surfaces on the screw shaft.
The lubricant-containing polymer members in the prior ball nut and screw assembly are, however, produced by mixing poly(.alpha.-olefinic) polymer with a lubricating oil, then melting the mixture with heating in a predetermined mold, and solidifying the molten mixture by cooling. Therefore, the lubricant- containing polymer members have necessarily required the complicated and high technology as well as the high production cost. In addition, it will be understood to those skilled in the art that the technology as to the ball nut and screw assembly may not be directly applied to the linear motion guide units without any modification. It is thus expected to develop an improved lubricating means for the linear motion guide unit what is referred to as a ball-spline, which makes it possible to keep self-lubrication even under too harsh situation for lubrication.